In an axial turbomachine, radial gaps between rotor blades and the casing lead to significant losses in thermal efficiency. In order to achieve an efficiency which is as high as possible, it is desirable to keep the radial gaps as small as possible at all operating points of the axial turbomachine. The axial turbomachine is a gas turbine, for example. During start-up and shutdown of the gas turbine, the radial gaps vary over time. Furthermore, the radial gaps vary during changeover from partial-load operation to full-load operation of the gas turbine. The gas turbine is conventionally designed in such a way that the radial gaps are of a sufficiently large dimension for the operating case in which the radial gaps are set at their smallest so that practically no contact occurs between the rotor blades and the casing. The consequence of this is that during continuous operation of the gas turbine unnecessarily large radial gaps have to be provided for this operating state, with which is associated a significant efficiency loss. the rotor, the rotor blades and the casing. Furthermore, the time-based variation of the radial gaps creates centrifugal stretch, especially of the rotor blades, transverse contraction of the rotor, possible play in the thrust bearing of the rotor, especially in conjunction with reversal of axial thrust during corresponding operating conditions of the gas turbine, and ovalization of the casing possibly occurring as a result of assembly-related prestressing and uneven heating of the casing.
It is therefore known to displace the stator blade carrier in order to set the gap width of the radial gaps. For example, laid-open specification DE 1 426 818 discloses an adjusting mechanism for displacing the stator blade carrier in the radial direction. To this end, eight longitudinally extending I-shaped segment carriers are distributed over the circumference of the axial turbine, the stator blade carrier being hooked on their inner end in a form-fitting manner. The surfaces which are in contact with each other of the flanges of the segment carriers and of the stator blade carrier are of a sawtooth-like design in order to convert a synchronous longitudinal displacement of all the segment carriers into a radial displacement of the stator blade carrier. With this, it is disadvantageous that on the one hand all the segment carriers are always to be moved synchronously in order to avoid tilting of the stator blade carrier in relation to the machine axis. On the other hand, the stator blade carrier must be designed in a segmented manner over the circumference, wherein the individual segments of the stator blade carrier are oppositely disposed, forming a gap, in order to be radially displaceable. Sealing of the gaps between the segments of the stator blade carrier is therefore very costly.
In addition, it is known from DE 10 2007 003 028 A1, for example, to axially displace the shroud ring of a gas turbine which lies opposite the rotor blade tips. For axial displacement of the shroud ring, this is of a conical form on the shroud side. A coupling ring which fits over the shroud ring is also conically foliated on the inner side. Between the two conical surfaces provision is made for cylindrical rolling elements which are oriented at an angle to the axial direction. As a result of a relative rotation of the coupling ring against the shroud ring the radial gap between the blade tips of the rotor blades and the shroud ring can be adjusted. In this case, the coupling ring, which is constructed with a relatively thick wall thickness, deforms the shroud ring, which is constructed with a relatively thin wall thickness, in the sense of an elastic deformation so that as a result of the rotation the diameter of the shroud ring can be adjusted and consequently the gap between the shroud ring and the rotor blade ring can be set. It is disadvantageous in this case that the shroud ring is elastically deformed. Also, a gap setting which is uniform over the circumference is only conditionally possible on account of the rolling elements which are distributed at a distance from each other.
Furthermore, for radial gap setting the axial displacement of guide components of a turbine by means of hydraulic pistons is known from EP 1 249 577 A1.